The present invention relates to surgical instruments, and more particularly to a surgical wrench for simultaneously driving a bolt and holding in place a part through which the bolt is driven, until the bolt has been tightened.
Although not part of the present invention, a basic understanding of surgical implants that may be installed using the present invention is important to the understanding of the invention. The Vermont Spinal Fixator (VSF) is one such device. FIG. 7 illustrates a Vermont Spinal Fixator device 10 in place on a spinal column. FIG. 8 is an exploded view showing the relationship of the various components of the VSF. The fixator device is designed to rigidly fix together two spinal vertebrae surrounding a fractured vertebrae and, thus, fuse the spine around the fractured vertebrae. The Vermont Spinal Fixator is disclosed in detail in Krag et al., An Internal Fixator for Posterior Application to Short Segments of the Thoracic, Lumbar, or Lumbosacral Spine, Clinical Orthopaedics and Related Research, 203: 75-98, (Feb. 1986), incorporated by reference herein.
In order to implant the fixator device 10, holes are drilled in the appropriate vertebrae through surface A overlying the pedicle on either side of each vertebrae. After the holes are drilled, pedicle screws 12 are screwed into the pedicle using a shaft handle which is attached to flats 16 provided on the top of each screw 12. Once the pedicle screws 12 are in place in each of the four pedicles, an articulating clamp 18 is attached to each pedicle screw 12 with a clamp bolt 20.
After the articulating clamps 18 are in place, the clamp bolts 20 are initially left somewhat loose to allow for the assembly of connecting rods 22 between the two pedicle screws 12 on both sides of the fractured vertebra. After the fractured spine has been appropriately aligned, the clamp bolts 20 are tightened to permanently fix the spine and isolate the fractured vertebra.
In the past, surgeons have had difficulty in starting the clamp bolts 20 in threaded holes 14 provided in each pedicle screw 12. Part of the reason for the difficulty is that the clamp bolt 20 passes through articulating clamp 18, which must be held in place while the bolt is started. In addition, the space between the spinous process B and the installed pedicle screw is limited and the incision made for this procedure is relatively small. There is generally not room for the surgeon to reach into the incision and start the bolt 20 with his fingers while holding the articulating clamp 18 in place. Additionally, the components are small and relatively slippery during the operation, rendering their manipulation by hand difficult even if sufficient room was available. The limited space between spinous process B and pedicle screw 12 makes the use of known wrenches problematic.
In the past, surgeons have attempted to hold the articulating clamp in place with forceps while spinning the head of the bold with another instrument. Although workable, this method is slow, cumbersome and technically very difficult.
Low profile wrenches for use in surgical procedures are known, such as the "Twin Cities Spinal Wrench" by the Twin City Surgical Company designed for use in installing threaded nuts on threaded Harrington compression rods. This wrench utilizes a flat meshing gear train for transmitting torque to an end gear having a open-end wrench configuration for receiving nuts to be torqued.
U.S. Pat. No. 4,374,480 to Diaz discloses an extension tool for torquing screw fasteners located in restricted access areas. The Diaz extension tool is provided with a flat meshing gear train wherein the gears are supported by being disposed in close fitting circular recesses instead of on shafts, in order to reduce the thickness of the tool. The first and last gears are provided with multifaceted recesses for receiving commercially available torquing tools.
These wrenches are illustrative of the prior art, which, in general, does not provide a device suitable for the task of installing parts fixed by threaded fasteners such as articulating clamps and clamp bolts in surgical implants such as the VSF.